1. Field of the Invention
The subject invention generally pertains to central vacuum systems and more particularly to a motor-cooling airflow path for such a system.
2. Description of Related Art
Typical central vacuum systems comprise a blower or vacuum motor that creates a vacuum within a stationary canister. A network of tubing usually connects the canister to several wall-mounted inlet ports that are installed at various locations throughout a house or building. A flexible hose can connect a portable vacuum tool to any of the inlet ports, so the tool can be used for vacuuming a floor or other surface. The vacuum motor draws dust-laden air in series through the tool, through the hose, through the tubing network and into the canister where the dust collects. The canister can be manually opened to empty it periodically.
There are two main types of central vacuum system: cyclonic and filtered. With a cyclonic system, structure within the canister directs the dust-laden air to circulate in a vortex, which employs centrifugal force to help separate the heavier dust particles from the air. A chute directs the separated dust particles to the bottom of the canister where they accumulate for later disposal. The vacuum motor draws the lighter clean air out from within the center of the vortex and discharges the air to atmosphere. Some cyclonic vacuum systems also include a filter.
In comparison, a filtered system includes a main filter instead of the vortex-generating structure. The filter blocks the dust particles while allowing clean air to be discharged to atmosphere. If the filter is in the form of a bag, the dust collects in the bag. Otherwise, the dust may simply drop from the filter onto the bottom of the canister for later disposal.
Many vacuum cleaners direct air across its motor to help cool the motor. The cooling air, unfortunately, may entrain carbon dust from the motor's commutator brushes and deposit a carbon residue on the exterior of the machine. To avoid this problem, some vacuum cleaners have a separate filter to help keep the carbon dust inside the machine. Examples of vacuum cleaners with a filter for carbon dust are disclosed in U.S. Pat. Nos. 5,685,894 and 5,412,837. Although such filters help keep the machine clean, they also create an airflow restriction that may lead to overheating.
Consequently, there is a need for a vacuum cleaner having a cooling airflow pattern that is suitable for use with a carbon dust filter.